1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, it relates to a package for an electrically programmable read-only memory erasable with ultraviolet rays.
2. Description of the Prior Art
FIG. 1 is a sectional view schematically showing the entire structure of a conventional semiconductor device including an electrically programmable read-only memory erasable with ultraviolet rays which is disclosed in, e.g., Japanese Patent Laying-Open Gazette No. 83351/1985. Referring to FIG. 1, the conventional semiconductor device including an electrically programmable read-only memory erasable with ultraviolet rays (hereinafter referred to as "EPROM") comprises an EPROM semiconductor chip 4 mounted on a lead frame and having an ultraviolet-irradiated surface upwardly directed, an ultraviolet-ray transmitting resin layer 6 formed on the EPROM semiconductor chip 4 for transmitting supplied ultraviolet rays, an ultraviolet-ray transmitting window 7 formed on the ultraviolet-ray transmitting resin layer 6 for introducing ultraviolet rays supplied from the exterior, an external lead wire 2 connected with the EPROM semiconductor chip 4 through a metal fine line 3 to serve as an input/output terminal for signals and synthetic resin layer 1 for protecting the semiconductor chip 4 against the environment or the like. Description is now made on memory erasing operation for erasing data stored in the EPROM as shown in FIG. 1.
In the semiconductor device as shown in FIG. 1, ultraviolet rays are directly applied to the EPROM semiconductor chip 4 from the exterior through the ultraviolet-ray transmitting window 7. The ultraviolet-ray transmitting resin layer 6 is adapted to prevent entrance of synthetic resin not transmitting ultraviolet rays into a space between the ultraviolet-ray transmitting window 7 and the EPROM semiconductor chip 4. In response to the supplied ultraviolet rays, the EPROM erases electrically written storage data. Detailed description of operation (e.g., discharge of charges from a floating gate) for erasing the storage data in the EPROM is omitted.
The semiconductor device as shown in FIG. 1 must be provided with the ultraviolet-ray transmitting window and the ultraviolet-ray transmitting resin layer, and hence assembling steps are complicated and it has been difficult to implement such a semiconductor device at a cost substantially identical to that of an ordinary semiconductor device sealed with synthetic resin. Further, the ultraviolet-ray transmitting window is not made of synthetic resin, and hence it allows entrance of moisture through its exposed interface, to be inferior in moisture resistance.
FIG. 2 schematically illustrates the structure of a non-rewritable PROM semiconductor device formed by an EPROM semiconductor chip sealed with only general synthetic resin having no ultraviolet-ray transmittivity. Referring to FIG. 2, the conventional non-rewritable PROM comprises a semiconductor chip 4 mounted on a lead frame, an external lead wire 2 connected with the semiconductor chip 4 through a metal fine line 3 to serve as an input/output terminal for signals and synthetic resin layer 1 for sealing the lead frame, the semiconductor chip 4 and the metal fine line 3. In the semiconductor device as shown in FIG. 2, memory erasability of the EPROM is aborted and the semiconductor chip 4 is sealed with the low-priced synthetic resin layer 1 transmitting no ultraviolet rays, thereby to realize a low cost. In this semiconductor device, the sealing resin material, i.e., the package 1 of synthetic resin has no ultraviolet-ray transmittivity, and hence storage data (memory contents) once electrically written in the PROM cannot be erased.
In the conventional semiconductor device as shown in FIG. 2, the sealing resin material does not transmit ultraviolet rays and hence the memory contents cannot be erased, whereby the function of the semiconductor device cannot be sufficiently tested in advance to delivery.
The aforementioned package for an EPROM having an ultraviolet-ray transmitting window is described in U.S. Pat. No. 4,460,915 entitled "A Plastic Package for a Radiation Sensitive Semiconductor Device," granted to Paul R. Engel.